fix: add fetch to the restore function (#2582)

lib/intercept.js

@@ -238,6 +238,8 @@ function removeInterceptor(options) {
 //  Variable where we keep the ClientRequest we have overridden
 //  (which might or might not be node's original http.ClientRequest)
 let originalClientRequest
+//  Variable where we keep the fetch we have overridden
+let originalFetch
 
 function ErroringClientRequest(error) {
   http.OutgoingMessage.call(this)
@@ -339,6 +341,9 @@ function restoreOverriddenClientRequest() {
     http.ClientRequest = originalClientRequest
     originalClientRequest = undefined
 
+    global.fetch = originalFetch
+    originalFetch = undefined
+
     debug('- ClientRequest restored')
   }
 }
@@ -437,7 +442,7 @@ function activate() {
     }
   })
 
-  const originalFetch = global.fetch
+  originalFetch = global.fetch
   global.fetch = async (input, init = undefined) => {
     const request = new Request(input, init)
     const options = common.convertFetchRequestToClientRequest(request)